The invention relates to a method according to the preamble of claim 1 for providing the edge of the starting sheet of an electrode used in the electrolytic refining or recovery of metals with a dielectric strip.
The invention relates to equipment according to the preamble of claim 16 for providing the edge of the starting sheet of an electrode used in the electrolytic refining or recovery of metals with a dielectric strip.
In the electrolytic refining and recovery process, which is used as a sub-process in the manufacture of metals, such as copper, nickel and zinc, a starting sheet made of, for example, stainless steel, aluminium or titanium is used as the electrode, and the metal to be refined is precipitated on the different sides of the sheet by means of an electric current. The metal that is accumulated on the surface is detached from the starting sheet at regular intervals. Generally, the electrolytic refining and recovery process is carried out in electrolytic tanks, which contain a sulphuric acid-bearing electrolyte and, alternatively immersed therein, plate-like electrodes, i.e., anodes and cathodes, which are made of an electrically conductive material. At the upper edges of the anodes and cathodes, there are lugs or rods, by which they hang at the edges of the electrolytic tank, and through which they are connected to an electric circuit and by means of which they are lifted into and out of the tank. The metal to be produced is either delivered to the electrolytic process in soluble, so-called active anodes, or in a form that has already dissolved in the electrolyte at a preceding process stage, whereby insoluble, so-called passive anodes are used.
Due to the electric current, the metal to be produced in the electrolytic refining and recovery process accumulates on all the conductive surfaces of the starting sheet, i.e., if the entire starting sheet is conductive, the metal to be produced covers, as a uniform layer, the entire part of the starting sheet that is lowered into the electrolyte. In that case, the deposits of the produced metal that are accumulated on the two sides of the starting sheet are, at three sides thereof, attached to each other over the narrow edges of the starting sheet and, therefore, the deposits of the produced metal are very difficult to separate from the starting sheet. To easily detach the deposits of the produced metal from the surfaces of the starting sheet, the deposition of the produced metal over the narrow edges of the starting sheet must be prevented, i.e., the edges of the starting sheet must be rendered non-conductive. The most common way of rendering the edges of the starting sheet non-conductive is to cover the edges of the starting sheet with parts, such as edge strips that are made of a dielectric material, such as plastic.
The publication WO/2005/057682 discloses a method of providing the edge portion of a sheet, such as the starting sheet of an electrode with a strip, such as a strip consisting of plastic material, by using equipment that comprises a die space. In this known method, the portion of the sheet edge is fitted inside the equipment that feeds the plastic material into the die space, the restrictive members and the die surfaces of the equipment preventing the escape of the heated plastic material out of the die space; the sheet and the equipment that feeds the plastic material are arranged so as to be movable with respect to each other, the portion of the sheet edge being located in the said equipment, and the die space of the equipment is heated during the process.
A problem with the solution disclosed in the specification WO/2005/057682 is the poor adhesion of the plastic strip to the edge portion of the plate-like component as a result of the shrinkage of the plastic material.
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